1. Field of the Invention:
This invention relates to variable magnification view finders, and, more particularly, to variable magnification view finders suited to be used in photographic cameras, or video cameras. Still more particularly, the present invention relates to the maintenance of a constant diopter of the finder during variation of the magnification of the finder image.
2. Description of the Prior Art:
In cameras whose photographic system and finder system are constructed separate from each other, when the photographic system is of the zoom type, it has been preferred, from the framing standpoint, that the magnification of the finder image is variable in proportion to the magnification of the image on the film. From another standpoint of its being built in the camera, it has been preferred that the finder be of reduced size, and its structure amenable to producing a desired range of magnifications of the finder image.
There has been a previous proposal for modification of the reverse-Galilean finder to a variable magnification one in such a way that the objective lens of negative power is divided into two parts of opposite power to each other, of which the rear or negative part is made to move toward the eyepiece of positive power to vary the magnification of the finder image, as disclosed in Japanese Laid-Open Patent Application No. SHO 53-63014.
Also in Japanese Patent Publication No. SHO 29-2927, not only the objective lens of the reverse-Galilean finder is divided into positive and negative parts of which the negative part is moved toward the eyepiece, but also the eyepiece is divided into positive and negative parts of which either one or both are made movable in that region of the range of magnifications which is associated with a large change of the diopter, thus providing a variable magnification finder.
These prior known variable magnification finders are, however, all imperfect in compensating for the diopter shift resulting from the variation of the magnification. So it has been difficult to obtain a good finder image throughout the entire range of variation of the magnification .